Canine Corona Virus (CCV) enteritis is a highly contagious disease in dogs with world-wide distribution. CCV gastroenteritis was first observed in February of 1970 in a U.S. Air Force patrol dog training school in Weisbaden, West Germany. In January of 1971, recurrence of the gastroenteritis disease syndrome was observed and the causative agent was identified as a CCV. In 1972 Cartwright and Lucas reported that antibody titers to transmissible gastroenteritis (TGE) virus had significantly increased in dogs after an outbreak of vomiting and diarrhea. It was concluded that TGE or more probably a serologically related virus such as CCV produced disease in these dogs.
Infection results from contact between infected and susceptible dogs. Infected dogs usually show symptoms of disease. However, dogs recovering from disease may shed virus in their feces and prove to be a continued source of infection for susceptible dogs.
In 1978 with the sudden outbreaks of Canine Parvo virus-induced enteritis, a renewed vigor and interest in canine enteric viruses was stimulated. First efforts were directed toward finding the causative agent for this new hemorrhagic enteritis-myocarditis syndrome which was severe and most often fatal. Upon investigation researchers discovered two distinct viruses, Canine Corona Virus (CCV) and Canine Parvo Virus (CPV). After further investigation the CPV proved to be the new agent, most often causing the highest morbidity and mortality. The CCV induced a disease somewhat similar but less often fatal. The simultaneous isolation of CPV and CCV has been reported. One survey that was conducted indicated that 17% of the cases of canine enteritis were found to be dual infections with CPV and CCV. Various state diagnostic laboratories confirm these findings.
Differentiation of Parvoviral and Coronaviral enteritis is difficult. The probable simultaneous infections with both viruses makes differentation even more difficult. In a serological survey in a kennel situation, 55% of the dogs tested were found to have been exposed to both CCV and CPV. Some kennels tested had up to 87% positive exposure to both agents. The severity of the enteritis attributable to simultaneous infection is unknown. However, one expert researcher in the field proposes that infection by both viruses increases the probability of morbidity in the dog.
As noted above, CCV enteritis is a highly contagious disease which has been observed on a world-wide basis. The incidence of CCV disease in family-owned dogs has been reported to range from 14.8% to 26%. The incidence in kennel-raised dogs ranges upwards to 30%. The incidence of gastroenteritis where both CCV and CPV were isolated is even higher. The disease can occur in dogs of any age. The importance of CCV gastroenteritis has seemingly increased with the outbreak of CPV gastroenteritis.
CCV gastroenteritis is characterized by a number of disease symptoms which have been compiled from the literature as follows: the first signs of disease are lethargy, anorexia and depression. The sudden onset of vomiting occurs in which blood can sometimes be found. Diarrhea can range from moderate to severe and projectile in nature. Diarrhea may persist for up to 10 days. The fecal material has a yellow-orange color with blood and mucus occasionally found therein. Moreover, the fecal material has a marked foul odor. The intestinal tract will contain watery, yellow-green material. Dehydration, weight loss and death have been reported. Protracted or recurring diarrhea may occur 2-3 weeks later. The severity of the CCV disease syndrome is thought to vary according to age, stress, environmental conditions, breed and concurrent infections. CCV has also been associated with respiratory disease symptoms of ocular and nasal discharge.
Both respiratory and enteric symptoms of disease have been seen experimentally by the present inventors. The symptoms observed have included a slight ocular discharge, a slight nasal discharge, diarrhea, weight losses, anorexia, dehydration, elevated temperatures and slight drops in both white blood cell levels and lymphocyte levels. Intestinal samples of infected dogs demonstrated that a significant degree of virus infection occurs following challenge.
CCV is a member of the Corona Virus group of viruses. Some pertinent characteristics of the Corona Virus group include:
(a) The virus particle is spherical or elliptical with knoblike projections on the outer surface of 18-20 nanometers (nm). PA1 (b) The viruses have very fastidious in vitro growth requirements. PA1 (c) The virus particle sizes vary in diameter from 80-200 nm. PA1 (d) The virus has a single stranded RNA nucleoprotein. PA1 (e) The virus develops in the cytoplasma of the cell. PA1 (f) There is a complex antigenic similarity within the group. PA1 (g) The virus density in cesium chloride (CsCl) is 1.24 to 1.26 g/ml.
Studies show that there do not appear to be distinct antigenic differences among various CCV isolates.
The veterinary community has recognized the need for a CCV vaccine but the literature indicates that little successful work has been done in this area. Experts in the field have recommended an oral-intranasal route of vaccination to insure not only the achievement of systemic immunity but also the obtention of local immunity in the intestinal tract.